4 weeks of flower. using jacks bloom booster for a nute. nuted water is about 6.4 ph from a dropper test.
Looks like sulfur deficiency. Are the leaf stems turning purple? Acute deficiency causes more and more leaves to develop purple leaf stems and yellow leaves. Treat this deficiency by fertilizing with a hydroponic fertilizer that contains sulfur. Lower the ph to 5.5 to 6.0. Add in organic sulfur to a fertilizer that contains magnesium sulfate (Epsom salts). Organic sources of sulfur include mushroom compost and most animal manures. Make sure to apply only well rotted manures to avoid burning roots. Source: Marijuana Horticulture Growers Bible by Jorge Cervantes (page 254)
it looks like either a nitrogen or sulfur deficiancy. for a nitrogen deficiency, the older leafs will yellow and die. the plant is redirecting the nutrient from old growth to promote new growth. so, if your old leafs are yellowing but new growth looks good then it is likely a nitrogen deficiany. give it any food containing nitrogen. for a sulfur deficiency it cant redirect the nutes from old growth to new because sulfur is an immobile nute. there for the yellowing will affect the entire plant tob to bottom including the new growth. to fix this : most cal/mag product contain large amounts of sulfur and will work fine. Epsom salts will work too as a folier and in the soil (mixed with water)